168 Dr. Thomas Thomson [Sept. 



The water actually obtained was 5* 17. This great excess of 

 water in the crystallized salt explains why its specific gravity 

 is so much less than that of the precipitated salt. 



Tartrate of Magnesia. 



This salt is easily obtained, by mixing solutions of tartrate 

 of soda and acetate of magnesia in atomic proportions. The 

 tartrate of magnesia precipitates. 



It is a snow-white powder, consisting of very minute 

 crystals. When moistened and dried slowly it is apt to 

 concrete into lumps. It is tasteless, yet a 'slight impres- 

 sion of bitterness is perceptible when the salt is kept for 

 some time in the mouth. Its sp. gr. is 1*960. 100 parts 

 of boiling water dissolve 0*6 of it; and its solubility is not 

 much inferior in cold water. 



The constituents of this salt, according to an old analysis 

 of mine, are as follows : 



1 atom tartaric acid . . 8*25 



1 atom magnesia . . . 2*5 



2 atoms water .... 2*25 



13- 

 Thus, in its constitution, it bears a striking resemblance to 

 racemate of magnesia. 



The bitartrate of magnesia has an acid taste, and crystal- 

 lizes in needles. It contains only 1 atom of water. 



I have been induced to give a description of the eight 

 preceding racemates, and the corresponding tartrates, to 

 enable the chemical reader to compare them with each 

 other. But it would draw out this paper to too great a 

 length were I to continue this comparison farther. 



IX. RACEMATE OF ALUMINA. 



To obtain this salt, 105 grs. of crystals of racemic acid 

 were dissolved in water, and the liquid was digested for 

 three weeks, in a flask, with 21*25 grs. of alumina, previ- 

 ously ignited. Not a particle of the alumina was dissolved, 

 but it was gradually converted into a bulky white powder, 

 a portion of which adhered obstinately to the glass. 



It was a snow-white, tasteless powder, insoluble in water. 

 When heated it decrepitates, and then becomes black, in 

 consequence of the destruction of the racemic acid. 



